1. Field of the Invention
The present invention relates to a method of and an apparatus for analyzing ions on a surface of a mask for semiconductor devices, and more particularly, to a method of and an apparatus for analyzing ions adsorbed on a surface of a mask using positive pressure effects.
2. Description of the Related Art
Circuit patterns on semiconductor devices are formed through a photolithography process. In such photolithography process, a photoresist film is deposited on a wafer, a pattern formed on a photomask is transcribed to the photoresist film by an exposure process, and the photoresist pattern is formed through a development process. Using the photoresist pattern, a film on the wafer is patterned to form a circuit pattern of the semiconductor device. In order to form the circuit pattern by the photolithography process, a mask, such as a photomask, is used. On a transparent substrate, such as light transmitting quartz, a shielding film such as light blocking chrome film is patterned on the photomask used for forming a circuit pattern in the photolithography process.
In order to manufacture a semiconductor device, an exposure process is carried out with many wafers using one photomask. When such repetitive photolithography process is carried out, unstable ions are produced during the process, and the unstable ions adsorb to a surface of the photomask by static electricity or chemical bonding. The ions adsorbed on the surface of the photomask not only prevent accurate transcription of the photomask pattern onto the wafers during photolithography process, but also produce identical repetitive defects on many wafers that are manufactured using the photomask.
Therefore, it is very important to remove the ions adsorbed on the surface of the photomask. Conventionally, ions adsorbed on surfaces of photomasks are removed by performing a cleaning process using sulfuric acid (H2SO4). While the cleaning process using sulfuric acid may remove the ions adsorbed on the surface of the photomask, sulfuric acid residues such as SO42− still remain on the photomask. In this regard, a method of removing the sulfuric acid residues by neutralization using ammonium hydroxide (NH4OH) has been used, but such method produces salt such as (NH4)2SO4 when neutralizing with NH4OH.
Therefore, in order to remove the adsorbed ions on the surface of the photomask through a cleaning process, the ions adsorbed on the surface of the photomask must be accurately analyzed. Conventionally, ions on the surface of the photomask are collected and analyzed by ion chromatography (IC).
However, when using the conventional method for ion analysis, it is not only difficult to analyze ions accurately, but also the variation of analysis results is large, thereby making it difficult to determine the cleaning recipe for removing the ions. Moreover, a significant amount of time is spent on collecting the ions, thereby increasing the ion analysis time.